If mobile phones start offering functions like digital broadcast reception and WLAN support, existing batteries will be too weak. Could fuel cells provide the answer?

About two years ago, the industry predicted that fuel cells in portable gear would be commercialized in 2004, and achieve widespread market penetration in 2005, eventually powering all portable systems. Even though 2004 has been and gone, though, the promised fuel cell-powered products have not yet arrived (Fig 1).

Most engineers in the fuel cell field seem to agree that the power source will not achieve commercial use until 2007, when regulations are relaxed to allow fuel cartridges to be carried onto aircraft. The problem of regulation is a major one when it comes to commercializing fuel cells, because even if everything goes smoothly it will not be possible to carry fuel cells into the passenger cabin of an aircraft until January 2007, at the earliest.

Another problem is how to ensure safety with regard to the methanol fuel, which is designated as a deleterious substance under the Japanese Poisonous and Deleterious Substances Control Law. Currently mobile phone and fuel cell manufacturers are beginning to work with the relevant government agencies, frantically trying to resolve these issues. Standardization of the fuel cartridges is also under way, and the industry is gradually preparing for full-scale release of fuel cells in time for licensing in 2007.

At the same time, though, as an engineer at one fuel cell manufacturer pointed out, "I really don't see the point is hurrying to commercialize fuel cells. It's not as if it can establish itself as a viable business."

This is a valid view, of course. Notebook personal computers (PC), which have been consistently cited as key candidates for fuel cells, can now run for up to nine hours continuously. The energy density of the Li-ion rechargeable batteries that make it possible is rising at 5 to 10% annually, and the power consumption of the PCs themselves is dropping.

In order for fuel cell manufacturers to invest in making fuel cells a commercial reality - accelerating development while resolving problems to do with regulations, assuring reliability and finding a suitable business model - portable equipment that absolutely requires fuels cells will be needed.

Mobile Phones as Driver
A number of mobile phone operators have said they are seriously considering fuel cells as power sources; the mobile phone therefore looks to be emerging as a key technology driver for fuel cell commercialization. In July 2004 KDDI Corp of Japan announced separate joint development plans with two vendors: Hitachi Ltd of Japan and Toshiba Corp of Japan. Shortly after, in September of the same year, NTT DoCoMo Corp of Japan disclosed that it had already prototyped a mobile phone fuel cell jointly with Fujitsu Laboratories Ltd of Japan, in March 2004. In October 2004, the largest electronics show in Japan - CEATEC Japan 2004 - was held, and KDDI and NTT DoCoMo competed with each other fiercely in fuel cell displays, each showing an apparently sincere interest in commercializing the technology.

There is a reason why mobile phone operators, originally not manufacturers at all, are all signing up for joint fuel cell development projects: they will be in a real bind when battery capacity becomes insufficient to handle rising mobile phone demands: terrestrial digital broadcasting tuners, frequency modulation (FM) radio tuners, miniature hard disk drives (HDD), wireless local area network (LAN) modules, and more. When broadcasting starts in 2006, terrestrial digital broadcasting is sure to have a major effect on mobile phones.

TV on Mobile Phones
There is without doubt some demand to watch terrestrial digital broadcasting on mobile phones, but there is little benefit to the mobile phone operators because reception does not use their communications infrastructure. In spite of this, operators are still eager to offer the new function. Mobile phones have always grown by adding new functions, and the frequency of mobile phone usage has risen with each new addition: E-mail, Internet access, video, and download services such as games and ringtones.

The places where key drivers such as E-mail and Internet access have been used - namely, inside trains and on station platforms - are the same places where people will want to watch digital terrestrial broadcasting. If, for example, the iPod portable music player from Apple Computer, Inc of the US were to come with a terrestrial digital broadcasting tuner, it is quite possible that people would spend more time on trains and station platforms watching the "video player" than using their mobile phones. In the worst-case scenario, this could mean that mobile phones devolve to merely tools for conversation again. This is why the mobile phone operators urgently want to offer terrestrial digital broadcasting reception functions, integrating broadcasting with their communications network.

Power supplies are beginning to emerge as a major obstacle to these goals, however. Existing batteries would only be able to support about two hours of terrestrial digital TV viewing, and after those two hours have passed even regular phone calls would be impossible. At the very least, according to a source at NEC TOKIN Corp of Japan, it is essential to at least double battery capacity, making it possible to watch two hours and still enjoy the same mobile phone conversation and call waiting times.

If mobile phones are equipped with miniature HDDs for storage and playback of music and video content, then battery capacity will have to be even larger. At this rate, the 10% annual capacity growth rate of Li-ion rechargeable batteries will not be sufficient (Fig 2). This is why NTT DoCoMo and KDDI are interested in the potential of fuel cells and are actively participating in development.

Mobile Phones: Huge Base
For the fuel cell manufacturers, this trend on the part of mobile phone operators represents an enormous business opportunity. If all mobile phones were to eventually use fuel cells, the market scale would be gigantic. Unit sales volume for mobile phone handsets by far exceeds that of notebook PCs.

While the motivation of fuel cell manufacturers has soared, there are still a number of naysayers, such as those who believe that fuel cells can't be made small enough to fit in mobile phones, or that there's no point in worrying about mobile phone applications until the fuel cell itself is commercially viable. And there is still considerable worry about whether or not users will actually accept fuel cell powered mobile phones.

The mobile phone operators are well aware of all these facts. In response, they are adopting a development strategy as summed up by NTT DoCoMo: "It will take time to develop fuel cells capable of being used in mobile phones, which is why we'll start with charger types." Mobile phone operators expect to find a solution, as KDDI explained: "Once the charger type is commercially available, we'll use surveys and monitors to gauge user reaction."

Wanted: "Power Eater"
A look back into history reveals that when batteries shifted from NiMH and Ni-Cd2 rechargeable to Li-ion rechargeable types, the situation was much the same as it is now with respect to fuel cells. The energy density was high, but there was considerable doubt in the industry concerning commercial viability, especially with regard to safety and reliability. In 1991, however, Sony Corp of Japan considered the new battery for its camcorder, and it began to appear in notebook PCs. In only a few years it had spread to mobile phones, digital cameras and a host of other portable equipment. One crucial factor in this success was the "power eater," a product or component with power consumption exceeding the capacity of older battery technologies. For the Li-ion rechargeable battery, the power eaters were camcorders and notebook PCs. When NiMH and Li-ion rechargeable batteries are compared, the major differences are that the latter has about 10% more capacity, and slightly less mass. To put this another way, if equipment can be found that requires that extra capacity, it is likely that equipment manufacturers will switch to the new technology.

Following Li-Ion?
Fuel cells will follow the same route to success as Li-ion rechargeable batteries. Terrestrial digital broadcasting reception is the power eater for mobile phones, and if fuel cells are the only plausible candidate at present then they have a significant chance to succeed even if performance is not significantly higher than Li-ion batteries (Fig 3).

Since the appearance of Li-ion rechargeable batteries, a wide range of portable equipment has come into existence utilizing the technology, such as digital cameras, personal digital assistants (PDA) and mobile phones. The Li-ion rechargeable battery played a major part in making these products possible. In mobile phones, for example, a variety of power-hungry components were added as battery capacity rose, such as color liquid crystal display (LCD) panels and camera modules. Fuel cells as well could not only bring TV viewing to mobile phones, but also provide major impetus to the further evolution of a range of new phones and the birth of yet newer devices.

The mobile phone does not seem to be the only power eater on the horizon, as designers for both digital cameras with video support and camcorders are beginning to complain about insufficient power. The video-capable digital camera from Sanyo Electric Co, Ltd of Japan, for example, currently handles 1 Gbyte-capacity SD Memory Cards and, combined with low-power design, can shoot for up to 60 minutes. SD memory card capacity is roughly doubling annually, however, which means that battery-drive photography time will have to increase to 2x in one year, 4x in two years and 8x in three years.

Performance Still Low
While mobile phone manufacturers have high hopes for fuel cells, actual performance is not very impressive yet. A source at KDDI commented, "We have nailed down the current capabilities of fuel cells through collaborative research," but performance is still far from satisfactory. This is why the first prototypes are external charger designs, increasing external dimensions to provide adequate capacity (Table 1).

The external charge-type models are still quite large. The prototype jointly developed by NTT DoCoMo and Fujitsu Laboratories, for example, measures 152 x 57 x 16mm. It uses an 18ml fuel cartridge for a single charge of an 800mAh mobile phone power supply. "We plan to develop a fuel cartridge capable of four charges," explained Fujitsu Laboratories.

Internalizing with Hybrids
Mobile phone operators plan to reveal a more advanced charger type in 2005, but the final goal is to pack the fuel cell inside the handset. As NTT DoCoMo puts it, "The technology will never achieve widespread use unless it's an all-in-one approach."

If the fuel cell unit has to fit into the dimensions of today's Li-ion rechargeable batteries, it would mean a size of 50 x 35 x 5.5mm. The fuel cell unit cannot utilize all of this volume, however. Fuel cells have difficulty handling load fluctuations, and as Hitoshi Morihara, manager, Fuel Cell Business Promotion Office, R&D Division of Hitachi explained, "In equipment with large load fluctuations, like mobile phones, an auxiliary power supply such as a rechargeable battery is needed." The average output needed to drive the equipment is handled by the fuel cells. The auxiliary power supply is added in when demand exceeds the average, and when consumption drops below average the fuel cell instead recharges the auxiliary power supply. This type of hybrid power supply must be developed.

Requirement: 60mW/cm2
The implementation of a hybrid power supply will of course require fuel cells, but also a small auxiliary power supply. The auxiliary power supply will also have to offer a high energy density. There are a number of candidates, including Li-ion, NiMH and Ni-Cd2 rechargeable batteries and electrical double-layer capacitors, but as it turns out the Li-ion batteries have the highest energy density and are the easiest to shrink. Rather than competing with fuel cells as power sources for mobile handsets, Li-ion rechargeable batteries will complement them.

The energy density of Li-ion batteries is expected to increase to 1.5 or 2.0x the present level within five years according to the battery manufacturers. In other words, by 2010 a Li-ion battery with the same capacity as one today will be only half the size. If you assume that half of the required output in the hybrid power supply will be provided by Li-ion batteries, and those batteries can be half the size of existing models, then that futuristic mobile handset will only need a Li-ion rechargeable battery one-fourth the volume of today's designs. And if that is the case, as NEC TOKIN added, "It should be possible to make film-type Li-ion rechargeable batteries. This would allow us to increase the area of the fuel cell, which boosts fuel cell efficiency."

If a Li-ion battery can be made as film measuring about 50 x 35 x 1.5mm, then the fuel cell unit can be as large as 50 x 35 x 4mm. If valves and other parts are kept to within 10% of the volume of the unit and an external fuel cartridge is used, then the fuel cell drops to 45 x 35 x 4mm. Assuming an output of 1W, the output density for the fuel cell would then be 63.5mW/cm2. This is about 3x to 4x the output density of direct-methanol fuel cells (passive designs without pumps or fans) being prototyped by a number of firms. If fuel cell performance can be boosted to this level then they will be able to handle the average demand for mobile handsets.

From NEAsia